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Reducing climate control loads in vehicles can improve our
nation's energy security, the environment, and public health. Peak climate
control auxiliary loads, such as a car's air conditioning (AC), put a
significant load on a vehicle's system. For instance, AC systems in
light-duty vehicles alone, consume 10% of our annual oil imports, which
factors heavily on our nation's energy security. Auxiliary loads can also
greatly increase a vehicle's pollution emissions.
At NREL we tackle this challenge by designing efficient
thermal comfort systems that keep you comfortable, while using less fuel.
We examine climate control system performance, occupant thermal comfort,
fuel consumption, and powertrain performance. Techniques include advanced
glazings, ventilation, air cleaning, energy-efficient heating and cooling
systems, and thermal comfort modeling. These approaches are applied and
evaluated in NREL's demonstration vehicle called the "Cool Car."
Using heat pipes to cool with less fuel
One successful approach shows that using heat pipes to
cool a vehicle's instrument panel (IP) significantly reduces cabin, IP,
and windshield temperatures, thus decreasing the need for AC.
The heat pipe system enables solar heat to evaporate water
in the copper pipes located under the IP, which cools the IP, cabin, and
windshield. The evaporated water moves convectively through the pipes to
the outside of the cabin where it condenses, releasing heat. The cooled
water returns under the IP.
Using this technique, cabin air temperatures were reduced
4°-6°C (observed during January and February), which could result
in a 15%-25% reduction in AC compressor power requirements. This
would increase fuel economy by 1.6-2.5 miles per gallon (mpg) in current
conventional vehicles with base fuel economies of 30 mpg. A 1-mpg increase
in fuel economy across the nation's vehicle fleet can save $5-6 billion
in fuel costs annually!
Turning waste heat into useful energy
Another promising technique is advanced thermoelectric
(TE) systems that turn wasted heat into energy. Approximately one-third
of the energy produced by current internal combustion engine vehicles is
lost as heat energy in the exhaust stream. This wastes tens of billions of
gallons of gasoline every year. NREL vehicle auxiliary loads reduction
team's research into advanced TE systems aims to recover some of this wasted
energy.
The team has developed a detailed advanced TE system
analysis model using MATLAB/Simulink software. The model allows quick
evaluation of numerous TE system design configurations and requirements.
Initial studies have quantified the performance and potential power output
of newly characterized TE materials at various locations along the exhaust
line and in a vehicle engine. Linked to NREL's ADVISOR vehicle analysis
software, the model shows the potential energy recovery and power output
for various drive cycles, engine types, and vehicle configurations.
NREL, industry, and other laboratory partners will continue
to work on advancing TE systems to convert exhaust waste heat into power to
run vehicle auxiliary loads such as pumps, fans, and lights; quantify the
benefits of current and future TE materials research; and identify system
design challenges in vehicles.
For more information, visit the Vehicle Auxiliary Loads Reduction
Web site.
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